Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $46.42   13.678%   $52.7693   $52.77   $52.75   $52.80  
  Purchase #2 $79.79   10.342%   $88.0419   $88.04   $88.05   $88.00  
  Purchase #3 $185.83   12.123%   $208.3582   $208.36   $208.35   $208.40  
  Purchase #4 $188.73   3.227%   $194.8203   $194.82   $194.80   $194.80  
  Purchase #5 $191.75   5.214%   $201.7478   $201.75   $201.75   $201.70  
  Purchase #6 $45.93   3.642%   $47.6028   $47.60   $47.60   $47.60  
  Purchase #7 $217.74   6.252%   $231.3531   $231.35   $231.35   $231.40  
  7 purchase totals = $956.19       $1,024.6934   $1,024.69   $1,024.65   $1,024.70